Five groups of weanling male rats were fed diets containing 20 % (by weight) of lard, its blend with palm olein (L/PO) and randomized oils (E-lard, E-L/PO), or soybean oil as the control, for 28 d. Comparative studies were made on liver microsomal enzyme activity related to the synthesis and parabolism of cholesterol, as well as cholesterol and its metabolites in the tissues and feces, and the physical and chemical properties of the dietary fats.
SFC curves showed the randomization of lard to hardly change in plasticity. Blending palm olein to lard showed faster melting behavior with rise in temperature, although there was greater hardness at about 5°C. Randomization of the blend resulted in analogous plasticity to lard. No significant differences in serum total and HDL-cholesterol concentrations could be detected among lard, E-lard, L/PO. E-L/PO and soybean oil groups. In all but the soybean oil group, most fatty acids excreted into feces were C16 : 0 and C18 : 0. They were relatively rich in dietaryfats, but the excretion of C16 : 0 was apparently inhibited, probably due to the unique triacylglycerol structure of lard, whose C16 : 0 preferentially occupies the 2-position. Microscopic observation of a cross section of liver indicated fatty droplets to be distributed more thickly in a region surrounding the porta than other regions in the soybean oil group. In the other 4 groups distribution was essentially the same. The excretion of cholesterol and its metabolites into feces was significantly higher in the soybean oil group, but almost the same in the other 4 groups. However, the ratio of total metabolites/cholesterol was basically the same in all groups. The activities of 3-hydroxy-3-methylglutaryl coenzyme A reductase and cholesterol 7 α-hydroxylase in liver microsomes with respect to a rate limiting enzyme of cholesterol-synthesis and parabolism, did not differ significantly among the 5 groups. The effects of lard, its blend with palm olein, and their randomized oils on cholesterol metabolism were thus concluded essentially the same as those of soybean oil.
